1. Field of the Invention
The present invention relates to a backlight unit which uses light emitting diode (LED) modules.
2. Description of the Related Art
Recently, with the rapid development of semiconductor technology, the performance of products is further enhanced while the size and weight thereof is reduced. Cathode ray tubes (CRT), which are still used for information display devices, have many advantages in terms of performance and price, but have a limit in miniaturization and portability. As a device for overcoming such a disadvantage, a liquid crystal display (LCD) device has been proposed. Since the LCD device can be reduced in size and weight and has low power consumption, the LCD device is being recognized as a substitute which can overcome the disadvantages of CRT. Currently, almost every information processing equipment requiring a display device includes the LCD device mounted thereon.
In the LCD device, a voltage is applied to a specific molecular arrangement of liquid crystal such that the molecular arrangement is converted into another molecular arrangement, and changes in optical characteristics of a liquid crystal cell, which emits light through the converted molecular arrangement, such as birefringence, rotatory power, two-color property, and diffusion, are converted into visual changes. That is, the LCD device is such a display device that uses the modulation of light by the liquid crystal cell.
Since the LCD device is a passive element which cannot emit light for itself, a backlight unit attached to the rear surface of a liquid crystal panel is used to illuminate the liquid crystal panel. The light transmittance of the liquid crystal panel is adjusted by an applied electrical signal, and still or moving images are displayed on the liquid crystal panel.
As for a lamp used in the backlight unit which supplies light to the liquid crystal panel, a cold cathode fluorescent lamp (CCFL) has been widely used. Recently, however, a backlight unit using LEDs are frequently used for a variety of display devices such as a portable device and a field sequential color LCD device.
Referring to FIG. 1, a conventional backlight unit using LEDs will be described in detail.
FIG. 1 is a perspective view of a conventional backlight unit.
As shown in FIG. 1, the conventional backlight unit is positioned under a display panel (not shown) and includes a plurality of LEDs 110, a plurality of LED modules 120 having a printed circuit board (PCB) which supports and drives the plurality of LEDs 110, an optical sheet 140 which is provided above the plurality of LED modules 120 so as to be spaced at a predetermined distance from the LED modules 120, and a heat radiating pad 130 which is provided on the rear surface of the LED modules 120.
The conventional backlight unit is constructed in such a manner that the optical sheet 140 disposed above the plurality of LED modules 120 is spaced at a predetermined distance from the LED modules 120, and one optical sheet 140 covers all the LED modules 120. In this case, the heat radiating pad 130 on the rear surface of the LED modules 180 may be divided in accordance with the number of LED modules 120 so as to be individually attached to each of the LED modules 120, or one heat radiating pad 130 may be attached so as to cover the overall LED modules 120.
However, when the optical sheet of the backlight unit is formed so as to be spaced from the LED modules, there are difficulties in achieving a reduction in size and thickness of a display device using the backlight unit.
Further, when the optical sheet for controlling light orientation is received and fixed as one sheet which covers the overall LED modules, the optical sheet above the LED modules should be entirely removed if any one of the LED modules is damaged. Therefore, a rework process of the backlight unit becomes complicated.